Dosage-dispensing devices for dosage material in the form of a powder or paste are used in particular to dispense small dosage quantities with high precision into small target containers. Such target containers are often placed on a balance in order to weigh the substance delivered out of the dosage-dispensing device, so that the substance can subsequently be processed further in accordance with given instructions. The dosage material is for example contained in a dosage-dispensing unit which includes in essence a source container and a dispensing head. Arranged in the dispensing head is a flow-regulating element, for example a slider gate, which upon actuation opens an outlet orifice. Passing through the outlet orifice which is connected to the source container, the dosage material can then flow into a target container which is arranged below the outlet orifice. The slider gate is preferably designed so that it can be coupled to a drive mechanism that is separate from the dosage-dispensing unit.
Dosage-dispensing devices of this kind are also often used to prepare mixtures of several individual substances. For this purpose, there is preferably a changing mechanism available whereby the individual dosage-dispensing units with the individual substances can automatically be set into, and taken out of, the dosage-dispensing device.
A dosage-dispensing device is disclosed in EP 1 947 427 A1 in which several dosage-dispensing units are arranged in a holder. The dosage-dispensing unit can be transferred between the holder and the receiving location of the dosage-dispensing device by means of a loading mechanism, for example an industrial robot. This solution has a serious disadvantage in that the entire system with its arrangement of individual separate modules requires a large surface area to set up, i.e. it has a large footprint. In laboratory facilities, especially in work compartments with exhaust systems, the footprint of any piece of equipment used inside the compartment is a central issue, as there are many of these compartments installed at users' facilities and space limitations are therefore a real concern. Furthermore, when such a comprehensive setup is installed, one has to anticipate a major project for the adjusting, cabling and programming between the dosage-dispensing device, the loading mechanism and the holder.
These disadvantages are in part countered by two versions of a dosage-dispensing device with a changing mechanism which are disclosed in EP 1 959 244 A1. In the first version, a holder for several dosage-dispensing units is movable along a linear path. The second version has a ring-shaped holder which is arranged so that it surrounds the dosage-dispensing device and can turn around the latter. Depending on the selection, for example based on a formula that is preset in the dosage-dispensing device, the individual dosage-dispensing units are moved into place one after another in accordance with their position number, they are coupled to the drive mechanism, and the substance quantities prescribed in the formula are dispensed into a target container. However, this arrangement still takes up a relatively large surface area as the changing mechanism is arranged at only a small height above the work surface, and the surface space below the changing mechanism can therefore not be utilized.
The different versions of a dosage-dispensing device with a changing mechanism according to the foregoing description are easy to produce, take up little surface space and, due to the fact that the changing mechanism device is incorporated in the device, can be put into operation without a major installation effort.
As an additional requirement however, in order to avoid contamination of the surrounding space and of the substance itself, the distance from the outlet orifice of a dosage-dispensing unit to the fill opening of a target container set on the weighing pan of the weighing cell should be as small as possible. This is of particular importance in the handling of toxic or highly reactive substances. It is preferable if a part of the dosage-dispensing unit that includes the outlet orifice at its lower end actually reaches inside the fill opening during the dispensing process, so that the area inside the rim of the target container is not contaminated with dosage material. This is not possible with the dosage-dispensing devices disclosed in EP 1 959 244 A1. To provide this capability, the entire changing mechanism would have to be height-adjustable. Consequently, the combined weight of all of the dosage-dispensing units that can be set into the changing mechanism would have to be moved vertically up and down. The large mass that would have to be moved could affect the speed of the individual steps in the changing of the dosage-dispensing units and could lead to increased vibrations. Furthermore, the entire space within which the changing mechanism can move needs to be kept free of other objects and other parts of the apparatus. Also, the holder cannot be moved during the dosage-dispensing process.
It is therefore the object to create a dosage-dispensing device whose requirements for surface area and for clear air space are small and which allows a fast change and a rapid loading of dosage-dispensing units or functional units.